The U.S. government is now urging owners of nearly 8 million cars and trucks to have the air bags repaired because of potential danger to drivers and passengers. But the effort is being complicated by confusing information and a malfunctioning website.

The government's auto safety agency says that inflator mechanisms in the air bags can rupture, causing metal fragments to fly out when the bags are deployed. The inflators are made by Japanese parts supplier Takata Corp.

Safety advocates say at least four people have died from the problem, which they claim could affect more than 20 million cars nationwide. On Wednesday, the National Highway Traffic Safety Administration added 3.1 million more vehicles to an initial warning covering 4.7 million cars and SUVs.

Car owners might have difficulty determining if their vehicle is equipped with the potentially dangerous air bags. The warning covers certain models made by BMW, Chrysler, Ford, General Motors, Mazda, Honda, Mitsubishi, Nissan, Subaru and Toyota.

Most of the 7.8 million vehicles are subject to existing recalls. But manufacturers have limited the recalls to high-humidity areas, excluding cars and trucks in states to the north. NHTSA says owners in Florida, Puerto Rico, Guam, Saipan, American Samoa, the U.S. Virgin Islands, Hawaii and "limited areas near the Gulf of Mexico in Texas, Alabama, Mississippi, Georgia, and Louisiana" should pay special attention to the warning.

Worse yet, the regulatory agency has twice corrected the number of vehicles affected and acknowledged that a list it released Monday wasn't completely accurate. The agency urged people to use its website to see if their cars are affected — but a feature allowing people to check for recalls by vehicle identification number malfunctioned Monday night and still wasn't operational Wednesday.

Automakers have been recalling cars to fix the problem for several years, but neither Takata nor NHTSA have identified a firm cause. The agency opened a formal investigation into the problem in June, and a theory put forth in agency documents suggests the chemical used to inflate the air bag can be altered by high humidity, making it explode with too much force while deploying.

"It's in a total state of uproar right now," said Clarence Ditlow, executive director of the Center for Auto Safety, a nonprofit advocacy group founded by Ralph Nader.

NHTSA Deputy Administrator David Friedman said in a statement that responding to the recalls is essential to keep people safe.

"It will aid in our ongoing investigation into Takata air bags and what appears to be a problem related to extended exposure to consistently high humidity and temperatures," he said. The agency, he said, is tracking down the "full geographic scope" of the issue.

Kathryn Henry, a spokeswoman for the safety agency, said it is unclear whether a high number of inquiries caused its website to malfunction. Until it's repaired, she urged car owners to go to manufacturer websites or call their car dealer.

General Motors, which sold two models with the faulty air bags, planned to notify about 10,000 customers by overnight mail. The models covered are 2003 to 2005 Pontiac Vibes in high humidity areas and Saab 9-2X models. The cars were made by other manufacturers — the Vibes by Toyota, and the Saabs by Subaru.

The rare warning by regulators comes three weeks after a Sept. 29 crash near Orlando, Florida, that claimed the life Hien Thi Tran, who suffered severe neck wounds that investigators said could have been caused by metal fragments flying out of the air bag on her 2001 Honda Accord. Her Accord was among the models beingrecalled.

One police agency concluded that the air bags caused her wounds, while another is still investigating. NHTSA is seeking information in the case.

On Monday, Toyota issued a recall covering passenger air bags in 247,000 older model vehicles including the Lexus SC, Corolla, Matrix, Sequoia and Tundra. Like many earlier recalls, Toyota's recall covers vehicles only in areas that have high absolute humidity. GM and Toyota each told customers not to let anyone sit in the front passenger seat until repairs are made.

Toyota said it's working with Takata to pinpoint the cause of the rupture and to gauge the influence of high absolute humidity, which is a measurement of water vapor in the air.

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List of affected cars as of 10/22:

BMW:

2000 – 2005 3 Series Sedan

2000 – 2006 3 Series Coupe

2000 – 2005 3 Series Sports Wagon

2000 – 2006 3 Series Convertible

2001 – 2006 M3 Coupe

2001 – 2006 M3 Convertible

Chrysler:

2003 – 2008 Dodge Ram 1500

2005 – 2008 Dodge Ram 2500

2006 – 2008 Dodge Ram 3500

2006 – 2008 Dodge Ram 4500

2008 – Dodge Ram 5500

2005 – 2008 Dodge Durango

2005 – 2008 Dodge Dakota

2005 – 2008 Chrysler 300

2007 – 2008 Chrysler Aspen

Ford:

2004 – Ranger

2005 – 2006 GT

2005 – 2007 Mustang

General Motors:

2003 – 2005 Pontiac Vibe

2005 – Saab 9-2X

Honda:

2001 – 2007 Honda Accord

2001 – 2005 Honda Civic

2002 – 2006 Honda CR-V

2003 – 2011 Honda Element

2002 – 2004 Honda Odyssey

2003 – 2007 Honda Pilot

2006 – Honda Ridgeline

2003 – 2006 Acura MDX

2002 – 2003 Acura TL/CL

2005 – Acura RL

Mazda:

2003 – 2007 Mazda6

2006 – 2007 MazdaSpeed6

2004 – 2008 Mazda RX-8

2004 – 2005 MPV

2004 – B-Series Truck

Mitsubishi:

2004 – 2005 Lancer

2006 – 2007 Raider

Nissan:

2001 – 2003 Nissan Maxima

2001 – 2004 Nissan Pathfinder

2002 – 2004 Nissan Sentra

2001 – 2004 Infiniti I30/I35

2002 – 2003 Infiniti QX4

2003 – 2005 Infiniti FX35/FX45

Subaru:

2003 – 2005 Baja

2003 – 2005 Legacy

2003 – 2005 Outback

2004 – 2005 Impreza

Toyota:

2002 – 2005 Lexus SC

2002 – 2005 Toyota Corolla

2003 – 2005 Toyota Corolla Matrix

2002 – 2005 Toyota Sequoia

2003 – 2005 Toyota Tundra